A. Goldstein (USRA) reports on behalf of the GBM-LIGO Group:
L. Blackburn (CfA), M. S. Briggs (UAH), J. Broida (Carleton College), E.
Burns (NASA/GSFC), J. Camp (NASA/GSFC), T. Dal Canton (NASA/GSFC), N.
Christensen (Carleton College), V. Connaughton (USRA), R. Hamburg (UAH), C.
M. Hui (NASA/MSFC), P. Jenke (UAH), D. Kocevski (NASA/MSFC), N. Leroy
(LAL), T. Littenberg (NASA/MSFC), J. McEnery (NASA/GSFC), R. Preece (UAH),
J. Racusin (NASA/GSFC), P. Shawhan (UMD), K. Siellez (GATech), L. Singer
(NASA/GSFC), J. Veitch (Birmingham), P. Veres (UAH), C. Wilson-Hodge
At the G297595 event time, GBM was taking data and viewing the entire
un-occulted sky approximately 67 degrees from Earth center (RA = 29.7, DEC
= +22.9), which includes 62% of the LIGO Bayestar LHV map.
There were no on-board triggers associated within a few hours of the GW
trigger time. The untargeted ground-based search of GBM data for
short-duration GRBs (Briggs et al., in prep) did not find any candidate
within an hour of the GW trigger.
The targeted search of the GBM data (, ) processes time scales of
0.256 to 8.192 s within 30 s of the LIGO event. This search identified a
hard transient on the 2.048 s timescale 16.6 s after the GW trigger with an
initial estimated False Alarm Rate (FAR) of 7.1e-5 Hz (90% confidence).
Using the assumption that an EM signal closer in time to a GW event is more
likely to be associated, the initial False Alarm Probability (FAP) is
estimated at 2.5% The localization of the event by the targeted search
(7700 sq. deg.; 90% containment) found that the LHV Bayestar map was
outside the 3 sigma statistical-only localization region. We can calculate
an associated FAR and FAP using this spatial information, however, the
FAR distribution that we have measured thus far assumes LIGO localizations
using L1 and H1, and may be different for the three-detector localization
maps. For completeness, we report the associated FAR including spatial
information as 1.7e-4 Hz (90% confidence) and FAP = 9.1%. The localization,
by itself, is highly suggestive of a Galactic source, encompassing the
location of two X-ray sources known to be currently active: Vela X-1 and
GRO J1008-57, however, the observed count spectrum is harder than typical
Although it has been determined that a systematic component to the GBM
localization uncertainty exists, this component has not yet been modeled
for un-triggered events. A follow-up human-in-the-loop inspection of the
lightcurve and the localization, incorporating the usual localization
systematic for on-board triggered events, reveals that the un-occulted
LHV map is still outside the GBM 2-sigma region, but within the 3-sigma
region. A ten minute lightcurve shows some evidence for flaring with the
localization of the flares consistent with the localization of this
 L. Blackburn et al. 2015, ApJS 217, 8
 A. Goldstein et al. arXiv:1612.02395
 V. Connaughton et al. 2015, ApJS 216, 32